The Shadow plays "Return of the Witch King" and also starts mustering elites in Angmar. He's pretty obviously going to Rivendell or the Havens.
The Free People pop back a dead hobbit to North Downs. When WK's army marches into Ettenmoors bound for Rivendell, Merry reacts by going Through A Day and A Night into Trollshaws! The WK attacks him, but Scouts run into Rivendell. The Shadow goes for Rivendell anyway, generating 35 attacks on the North unit inside, driving the North to war.
Ordinary cost of getting the North to war: 3 musters, 0 cards. This cost of getting the North to war: 1 event, 1 other die, 2 cards.
On the plus side, that elite + hobbit helped in the defense of Rivendell.
On the minus side, if the Shadow just walks away, then there's no causus belli for the North.